1. Field of the Invention
The present invention generally relates to screen printing and more particularly to an improved paste nozzle that includes two layers, where the inner layer is softer than the outer layer.
2. Description of the Related Art
Thick-film metal-mask screening requires an extrusion-type nozzle for applying paste to stencil masks to produce personalized conductive thick-film features including conductive lines and filling thru vias. One example is U.S. Pat. No. 6,132,510 (incorporated herein by reference) in which a single-layer compliant nozzle is disclosed. Conventional nozzle design primarily enables the formation of thick, high definition features, and secondarily preserves the stencil mask integrity. For high line definition, a rigid contact surface is preferable. To the contrary, for long mask life, high nozzle contact surface compliance is needed. The compliance achievable with single-layer compliant nozzle is limited by the requirement that the nozzle not scoop paste out of the stencil during screening or get abraded by the mask surface. Conventional nozzles focus primarily on line definition, resulting in poor mask wear characteristics. The present disclosure seeks to satisfy both goals, enabling high quality stencil screening with very low stencil wear characteristics.